Steel manufacturers have been sampling parts of the steel sheet for shipping out and provided the results of tensile tests to users as material information. At the same time, defects and other quality information, for example as described in Japanese Patent Publication (A) No. 2003-215052, is being supplied as defect inspection results together with images and positional information in the longitudinal direction of the steel sheet to users as electronic information through computers.
In the above way, usually the tensile tests of steel sheet have been performed by sampling parts of the steel sheet shipped out. The tensile tests are run off line, so only the mechanical properties data of the sampled parts of the shipped out steel sheet can be obtained. If trying to obtain detailed material information on the shipped out steel sheet, it would be necessary to take a large number of samples for tensile tests. For this reason, the steel sheet would have to be finely divided and, accordingly, it would no longer possible to meet the predetermined shipment weights. Further, even if taking a large number of steel sheet samples, tremendous time and effort would be required for the tensile tests. This would not be practical.
On the other hand, quality information like surface defects is detected by surface defect detection devices installed on the steel sheet production lines. The data is compiled by computer and can be provided to the users through a network.
However, for the yield strength, tensile strength, and other mechanical properties, the only means for measuring the mechanical properties is to take steel sheet samples and test them for mechanical properties. It is impossible to provide the users with these mechanical properties for entire lengths.
Further, in some places, r-value detection devices using non-destructive, magnetic flux measurement have been installed on the steel sheet production lines, but adjustment is required for each type of product such as mild steel sheet or high-tensile steel sheet and only specific mechanical properties could be measured, so these were not universally applicable.